Appliance Design - March 2009 - (Page 20)

POWER Battery Electrochemical capacitors hike peak power in portable applications. Boost E lectrochemical capacitors are a relatively new contender in the energy storage ball game. While electrochemical capacitors are related to batteries, they use a different energy storage mechanism. Batteries move charged chemical species (ions) from one electrode to another through an electrolyte. The ions interact chemically, i.e. undergo chemical reactions with the electrodes, to store energy. These reactions take time and limit the peak power batteries are able to provide. By contrast, electrochemical capacitors store electrical charge physically, without using chemical reactions. Because the charge is stored physically, the process is highly reversible, and millions of charge/ discharge cycles are possible. Of more interest for the applications discussed here, however, is the fact that no time consuming chemical reactions are occurring, so electrochemical capacitors can move energy in and out quickly. Their power densities (W/kg) are 100 to 1,000 times higher than even advanced battery technologies. This is shown in the Ragone Plot in Fig. 1. In addition to electrochemical capacitors having high power density and lifetimes of more than 1 million charge/ discharge cycles, they also require no maintenance and they work well over broad temperature ranges. Before exploring how to design them into a circuit, one should first understand how electrochemical capacitors operate. An electrochemical capacitor does not store energy between two plates like a traditional capacitor. Instead, it stores energy within an electrical double-layer that forms at the electrode/electrolyte interface. The capacitance is directly proportional to the area of the electrode and inversely proportional to the distance between the layers of charge as shown by Equation 1. This shows that the combination of extremely high surface area with extremely small charge separation allows electrochemical capacitors to store orders of magnitude more energy than traditional capacitors. Most electrochemical capacitors (also known as supercapacitors or ultracapacitors) are manufactured using high surface area carbon as the electrode material. Some designs utilize less expensive Equation 1. C A d By mark daugherty, kevin leonard, and wendy suyama Mark Daugherty is CEO, Kevin Leonard is CTO, and Wendy Suyama is senior chemical engineer, SolRayo LLC, Madison, Wis., a division of Enable IPC. 20 applianceDESIGN March 2009 www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - March 2009 Contents Editorial Shipments/Forecasts News Watch Transmitting Power Wirelessly Promises to Reduce the Ever-Growing Tangle of Cords and Cables Found in the Modern Home. There Are Different Technological Approaches for Achieving this Goal, and Some Are Already on the Market. Electrochemical Capacitors Can Provide an Extra Peak-Power Boost in Battery-Operated Appliances, Allowing Product Designs to Have Smaller Battery Packs. Metallic Foams Put the Properties of Metals into Lightweight Packages. Applications for this Emerging Technology Include Gas Burners, Heat Exchangers, and Electronics Housings. Hall-Effect Switches Are Compact and Provide a High Degree of Reliability and Durability as They Virtually Eliminate Mechanical Wear, Shock, and Contact Oxidation. Blowing Agents for Polyurethane Foam Insulation Face Increased Scrutiny Due to Global Warming Concerns, but Alternatives with Lower GWP Values May Provide Solutions to Meet These Challenges. Design Marts Association Report: AHAM Advertisers' Index

Appliance Design - March 2009

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